Does the audio an instrument emits above 20 KHz affect how the instrument sounds?

Question

It's commonly held that humans can hear sounds in the range 20 Hz - 20 KHz.

But most acoustic instruments will emit sounds outside that range, for instance breath sounds from flutes and recorders, bow noise on bowed string instruments, plucking noise on plucked string instruments, and so on.

One strand of reasoning says that if an instrument produces sounds with components above 20 KHz then they're inaudible and so don't really matter.

But is that true? Does the ultrasonic part of an acoustic instrument's spectrum affect its perceived sound?

I'm specifically asking about acoustic instruments and what it's like to be in the same room as that instrument as it's performed. I'm specifically not asking about audio recording/storage/replay, as that's a whole subject on its own.

This question was prompted after hearing a program Costing the Earth on BBC Radio 4 last night which reported that in the rainforest there's significant ultrasonic sound and that's why we feel better there than in the urban environment.

Subsidiary Question Seems no-one has the answer at their fingertips. I've been wondering what experiment would answer this question?

Answer 1

As far as I know up to this point there is exactly 0 scientific indication that any human will perceive music differently due to ultrasonic sound content, no matter what turntable producers want to make you believe.

High frequencies of certain parts of instruments might affect the sound due to non linearity. E.g. an Aetherophone uses a very high frequency oscillator mixed with a second high frequency oscillator, which produced the difference frequency which might then be audible.

But generally this will rather affect low frequencies than high ones, as high frequencies experience more dampening, and less effects will actually result in an audible distortion.

But the high frequencies actually emitted by the instrument – most likely no.

Answer 2

As most of what we hear of other people's instruments is from a recording, most of this becomes moot anyway.

If you're in the room listening, you're still not hearing what the mic hears. Just try standing near a drum kit in a recording studio, then comparing it with what the control room hears for an extreme example.
Don't try this at home - by putting your ear 1" from the snare head, you'd get what the mic gets… except the mic won't even blink at those SPL levels [120 - 140 dBSPL potentially]. You, on the other hand, will suffer at least some temporary, it not permanent, hearing loss & will have experienced more pain than 'hearing'.

If you've got a violin on your chin, then half of what you hear is distortion in the nearest ear - you don't notice it because you're used to it. If you're trapped in a small room with one, it makes your teeth squeak.

So… where do we measure this possible high frequency 'interference' that we may or may not be able to perceive? Inside the instrument, 1/2" from it, far enough away that we're getting a good amount of room reflection in it, outdoors, in an anechoic chamber? Take your pick.

My best, flattest mic [so good they took one to Mars in 2020 to capture sound, I kid you not] is only good from 20 - 20kHz. You can get mics that go higher, but they tend to be for specialist use, not for music.

Answer 3

Simple answer, most likely not - to humans.

There must be many, many sounds out there that are sounds, but are inaudible to humans. Most, it figures, we are unaware of, for obvious reasons. Dog whistles, for example. We know they work, as they have an effect on dogs, but we're blissfully unaware of the racket they make to dogs!

As we know, most instruments will not only produce the fundamental sound of a note, but varying degrees of its harmonics. An interesting point would be how that sound (due to its harmonics) would be 'heard' by different individuals. Some time ago, I built a speaker cab with an 18" speaker and a horn tweeter. The band members could hear the white noise emanating from the tweeter - I was blissfully unaware! So we heard the sound even when notes were played, in different ways.

So, basically, no, and speakers, headphones, et al, which are said to reproduce sounds outside the human hearing range may well do so, but they're as much use as the anti-elephant paint on my chimney pot...

Answer 4

There's some evidence that ultrasonic frequencies are in fact audible! https://en.wikipedia.org/wiki/Ultrasonic_hearing

But I think most arguments for reproducing frequencies above 20Kz come from the fantasy world of Russ Andrews. https://www.russandrews.com/

There's also the issue of what happens when you sample with a Nyquist frequency TOO close to the top of audible range. There's no true 'brick wall' filtration.

Answer 5

One can start with the fact that the nominal 20kHz limit is somewhat different between individuals and some (esp. younger ones) are sensitive to a kHz or two above 20.

Could this make difference exactly in regard to music is an open question.

I personally can hear up to e.g. 15kHz, but cannot really distinguish the pitch of a single tone between 7kHz and anything above. It may be generally impossible or a matter of training, I don't know. Even if it is a matter of training, probably few people will have it.

On the other hand, human ears (and the processing circuity between them) are known to be non-linear in a number of ways.

Loud sounds (and even not so loud ones) are known to alter the sensitivity of the ear outside of the sound's own spectrum, so e.g. an ultrasonic beat could leave auditory artifacts over the usual, audible sound.

Again from personal experience, the ultrasonic rat repellents (be damned whoever invented them) make me almost deaf even if set at frequencies that I am unable to hear.

In short, one can hear artifacts of an ultrasound even if unable to hear the ultrasound itself. The effect is small and I think it will be cruel to the listeners to use it even if possible.

Answer 6

It is possible to hear ultrasonic sound under the right circumstances, essentially if you have interfering ultrasound waves that generate beats at a lower frequency. This can be used to transmit audible sound directionally, some key words are "parametric speakers", "audio laser" and "beam forming".

As explained on directional-loudspeakers:

The speaker array actually produces a modulated wave made of two separate ultrasound waves. One of them is a steady, reference tone of a constant 200,000 hertz (Hz) frequency (the carrier wave) and the other is the signal that fluctuates between 200,200 Hz and 220,000Hz (the modulating wave). Although they're combined, it's easiest to think of them as two separate waves traveling out in parallel straight lines through a column of air without overlapping. If they meet an obstruction (such as your curious head), they suddenly slow down and mix together so they interfere constructively (by adding together) and destructively (by subtracting from one another). By the principle of wave superposition, two ultrasound waves of those frequencies can subtract from one another to produce a third wave with a much lower frequency in the range 200–20,000 Hz—and that's in the frequency range that your ears hear.

Could it be that interferences of ultrasound waves therefore effect how a music instrument sounds? I think so.

Can it be experimentally tested? It is tricky, as in the explanation above: As soon as these interfering ultrasound waves hit an obstacle (such as an eardrum or a microphone) they turn into regular sound waves, so even if you record a full audio spectrum from 16Hz to 200 kHz, these would be recorded at the lower interference frequency. Therefore filtering out the high frequencies would not change that. What should be possible, at least in theory: Record only the ultrasonic part of the spectrum (or record the full spectrum and filter out the audible frequencies) and play it back. Whatever is audible then would be the contribution of the ultrasound frequencies to the sound of the instrument. Whether or not that is technically feasible, I don't know.

Answer 7

I find the question VERY theoretical. The given frequency range is just the extension of the sequence of harmonics, which will surely be influenced by any constructional modifications you may attempt to strenghten or weaken the supersonic parts. But with changes already in the easily hearable harmonics, how to decide (beyond recording/low-pass filtering which may have more impact than the effect you are searching for)?

Answer 8

Not in any direct sense, but there's an indirect sense where it might matter: all of the sound (audible and inaudible) is physical movement, and all of it is energy given up to the atmosphere by the instrument. So if you were to take an instrument and modify it to make more or less ultrasound, you might find that doing so alters the timbre of the instrument in ways that you wouldn't expect from a simple analysis.

The tension on a drum's head could evolve differently, giving it a different "note" and a faster or slower decay. The distinctive sound of bells and gongs is caused by the amplitudes of a large number of different resonances evolving over time (transferring energy between each other) after the instrument is struck, and any ultrasonic resonances would have an effect on that. A bowed instrument might exhibit a different amount of friction between the string and the bow. And so on: musical instruments are complex and nonlinear.

I'm not qualified to say whether any of these effects are significant — I'm not an expert in the field and I would love to hear from someone who is — but I would be very surprised if none of them were.

Answer 9

I would say yes and no. If there is an ultrasonic frequency or fundamental, it would have harmonics which you will hear because of the ultrasonic part. However that sound can be produced with out ultrasonic wavelengths. So it’s still sub 20khz that you hear. But higher then 20 kHz still effects and resonates with lower frequencies and produces new sound you will hear but in the sub 20 kHz region and so these harmonics do not require super 20 kHz fundamentally but are naturally produced by them where there is harmonics.

So I think in working reality the simplest answer is yes. They can definetly effect the sounds you hear though you can not hear them alone.

Further if the given the ultrasonic frequency, frequencies which divide the ultrasonic frequency, will have a harmonic and the amplitudes will be effected at a given frequency which divides the ultrasonic frequency. You may hear this lower frequency that divides the ultrasonic frequency get changed. All the common divisors will be effected. But because the high frequency happens more times per second, it will have smaller and smaller effect as the area of the amplitude of the wave gets smaller and smaller. There is less power per amplitude.

So you would think that these ultrasonic waves probably in natural occurrence become less and less important in the sound we hear. But with digital audio or anything specifically designed to utilize these ultrasonic regions to hit harmonics, they certainly can have hearable effects.

It is also interesting that because you can not hear these frequencies on their own they can be used to construct harmonics, that can’t be constructed and sound the same- as with waves using audible wave lengths.

Thus ultrasound is not totally insignificant, in sound and music.